Potential new RMH design questions

Because I am new to Permies and not finding the answers I am needing, I am piggy-backing off this RMH forum. If this needs to go somewhere else, please help me learn where that should be. My questions are related in the sense of a new design need for myself. All designs and builds that I've seen are based on a mass in a bench style. For me this would take up too much floor space. What I want to do is eliminate the bench completely and simply create an interior partition wall of mass. In other words I want the mass to be the wall itself between the main living area and a bedroom/bathroom space. Can the RMH mass be vertical like a wall? If the wall is 100% brick and only thick enough to house the flue pipe or brick shaped flue channels, zig-zagging back and forth up to about seven feet high and 14 feet long as the flue gets higher in the wall? The exhaust would be at the top of the wall.

Do you think enough mass could be accumulated with only one brick's width on each side of the flue space but going up for about seven feet high? I hope this makes sense. If not, please ask whatever clarifying questions you need. The questions will probably help me to better visualize and articulate what I am trying to accomplish. The overall dwelling will be a 16' x 40' low ceiling cabin style building. About 25 feet would be open for the kitchen/dining/living area and the other 15 feet would be the bedroom/bathroom/closet/storage area. Several hundred gallons of water will be stored in the non-visible loft space, providing a gravity fed water system for kitchen and bath areas. The space above the ceiling and below the roof will receive sufficient heat from the living space below (all from the RMH) to prevent the water tanks and lines from freezing. The exterior walls are of a unique design comprised of standard 2x4 vertical studs with 2x2 horizontal boards on the inside every two feet from floor to ceiling. This prevents the transfer of outside cold (or heat) to the inside through the wood. The floor, walls and roof will all be insulated with spray foam. Hopefully this information will become useful to many others as well as myself. Thanks to all who have something useful to say about this idea. I hope to begin next spring.

The wall doesn't need pipes, just a cavity to hold the gases. A flue would take air from near the floor where the coldest gases are. But the heat would be gathered at the top of the wall where you may not want it.

Hi Jim; Welcome to permies!
Great that you want to heat your home with a rmh!

Do you have a copy of the RMH builders guide ? Written by Ernie & Erica Wisner it is readily available on Amazon or from them direct. Its the go to book for any rmh builder.

Have you built one before? Were you thinking of a J tube or a Batch box? Were you planning on ceramic fiber or firebricks to build your core?

One brick thick on either side of your flue really isn't much mass. You might want a least 2 bricks wide on each side.

One issue I see is having to disassemble your wall if you have problems. Hopefully this is a non load bearing wall? Have you looked into brick bells ? They have a much smaller but taller footprint than a horizontal mass. They work very well , similar to a Russian masonry stove.

Keep us posted on your build. The rmh portion should stay in this forum , if you liked we have building forums where you could discus your build and post progress photo's once it commences.

Excellent video max! Thanks for sharing , that might be just what Jim is looking for!

Not all who wander are lost... J.R.R. Tolkien

Graham Chiu

Posts: 447

Location: Wellington, New Zealand

14

posted 9 months ago

And Peter's Free University build

Jim Higgins

Posts: 6

1

posted 9 months ago

Thanks to all the contributors so far. I am a little familiar with a bell chamber but as mentioned, this is not the effect that I am after. I need the entire wall to be a warm source. It also sounds like I might need to make the flue wall not the full 7' but this will be discovered for real when I am able to actually build. If this is the case then I will simply finish the upper part of the wall without flue space. Either way it will not be load bearing but a simple partition wall to separate the two areas. It also seems that I will need to make the wall thicker than first thought.

I have not built any heaters yet nor do I have the book yet. Both are planned before the actual cabin build. I will provide more info when the time comes. Again, thanks to all.

Jim

Graham Chiu

Posts: 447

Location: Wellington, New Zealand

14

posted 9 months ago

2

A bell I believe just refers to the container of the gases. So, if you had a double wall with the gap holding the gases, then that's still a bell.

Jim Higgins

Posts: 6

1

posted 9 months ago

Sorry for the duplicate post. I'm still learning how to use these forums. Is there a way to reply to a specific post rather than just adding another post at the end of whatever has been posted by everyone so far?

Jim Higgins

Posts: 6

1

posted 9 months ago

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Thanks Graham. I understand the concept of the bell being just a chamber holding the gases. The problem for my intent is that all the heat is kept at the top of the bell while the cool air is at the bottom. I need the whole wall to be warm. This is why I believe I will go with ducted space whether that is via metal duct work or simply building duct space with the brick or other material I end up using. With the duct work, at least as I understand now, all heat travels the entire duct work, thus heating the mass all along the way. If the ducted spaces progress upward instead of around and back (however many times) in a low bench, the heat will build up from the bottom to the top of the wall where the exhaust will exit and go through the roof. If my understanding so far of the premise behind the ducting principle is wrong, I would appreciate some explanation. Since I have not yet read the work books available I realize I may be blowing smoke ;-}

Satamax Antone

gardener

Posts: 3040

Location: Southern alps, on the French side of the french /italian border 5000ft high Southern alpine climate.

134

posted 9 months ago

2

Graham Chiu wrote:A bell I believe just refers to the container of the gases. So, if you had a double wall with the gap holding the gases, then that's still a bell.

Not exactly.

A bell, to act as such, has to be of a certain volume, to let the convection happen, and avoid bypassing. The absolute minimal floor surface area has to be over 5 times the CSA to avoid bypassing.
In case of a wall, is is easily attained. If not too thin.

Jim Higgins wrote:Thanks Graham. I understand the concept of the bell being just a chamber holding the gases. The problem for my intent is that all the heat is kept at the top of the bell while the cool air is at the bottom. I need the whole wall to be warm. This is why I believe I will go with ducted space whether that is via metal duct work or simply building duct space with the brick or other material I end up using. With the duct work, at least as I understand now, all heat travels the entire duct work, thus heating the mass all along the way. If the ducted spaces progress upward instead of around and back (however many times) in a low bench, the heat will build up from the bottom to the top of the wall where the exhaust will exit and go through the roof. If my understanding so far of the premise behind the ducting principle is wrong, I would appreciate some explanation. Since I have not yet read the work books available I realize I may be blowing smoke ;-}

Well, the exhaust of a bell is not at the top, but at the bottom. It's like an inverted siphon. Gases enter the bell at the bottom, rise to to their buoyancy, since they are hotter and less dense. cool down at the contact of the surrounding mass, sink back down towards exhaust at the bottom.

Heat, in the mass travels in all directions. So your whole wall will be hot after a while.

If you want the wall to be all heated more evenly, you make it a double bell. Top and bottom one.

The brick bell on my 5" RMH gets warm right down to floor level when heated for some time. The top is appreciably hotter but the whole bell is providing useful heat.

I'm sure a 'thin' bell (essentially a hollow wall) would be very effective.

Jim Higgins

Posts: 6

1

posted 9 months ago

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Thanks for the additional information and resources. This helps me to understand some of the principles better. Unfortunately the graphics did not download with the text so some principles are not as clear as they would have been. I definitely need to get the workbook as soon as possible.

The initial question has been well answered in that a partition heater wall can certainly be built. Now, learning how to make it the best for heating multiple areas is what I need to experiment with. What a great resource this is.